Present processes for the production of wooden steering wheels produce steering wheels which, despite the extra cost, are often unsatisfactory in appearance and stability. In addition, current methods are technically and economically less suitable for the production of such steering wheels, with aesthetic looking veneer grains such as burl-veneer or multi color.
The common process used in producing wooden or wood based steering wheels for motor vehicles involves using wood-veneer with a thickness of about 1.5 mm, about 4000 mm in length (from a roll or sheet) and about 100-200 mm in width. The veneer cuttings are laminated into a circular shape by rolling them around a steel core after the application of cold, liquid urethane bonding material (glue). The rolls are then clamped together and placed into a curing oven for a period of about 10-15 hours.
After the curing step, the rolls are horizontally sliced into half segments arcs. A recess, corresponding in dimension to the steering wheel rim, is then routered onto the segments (generally with a numerically controlled router). A final length of the segment is then cut and assembled on a tubular steel core with the segment arcs being glued together over the tubular steel core. After a sufficient curing time, the segments are machined, in situ, into their final shape with a numerically controlled router and various cutting tools.
The present process entails many shortcomings among which are the application of liquid glue to the veneer, which uncontrollably affects the moisture content thereof and dimensional stability of the laminated parts. In addition, the rolling of the veneer around the forming core is effected without controlled pressure thereby resulting in the varying strength of the veneer with uneven deformation tendencies relative to the laminated part. Once the laminated rings are cut into segments, as described, there is also a natural tendency to return or "spring-back" to their original unstressed form, thereby tending to increase radius, often in an uncontrolled manner and to an uncontrolled extent. As a result, the position of the wood segment on the steering wheel can vary markedly and, when taken in conjunction with a pre-established program for machining, the final position of the wood-segments over a steering wheel is not predictable or controllable. In addition, since the outer form is machined after the assembly of the wood-segments thereon, it is technically (without any realistic economy) difficult to laminate burl-veneer over the segments.